In the context of vehicle finishing, plastics have become established as materials for vehicle parts and also for both interior and exterior vehicle accessory components and components for installation in or on the vehicle. Plastics, just like other materials, are coated, or painted, for decorative reasons (coloring, for example) and/or for technical usefulness (light stability and weather resistance, for example) with corresponding coating compositions. An important prerequisite for a high-quality coating is the adhesion to the substrate, in other words the underlying surface. It is common knowledge that particularly in the coating or painting of plastics, adhesion problems to the plastics substrate, in some cases serious, may occur. To achieve acceptable adhesion of the coating composition in question, such plastics are conventionally subjected to a surface-activating pretreatment. The most frequently employed methods are flame treatment, plasma treatment, and corona discharge.
Also known for the purpose of improving adhesion is the use of adhesion promoter substances, especially chlorinated polyolefins. From an environmental viewpoint, however, their use is very deleterious.
The adhesion promoter substances are employed for example via adhesion primers, which comprise the adhesion promoter substances and which are applied to the plastics substrate in a separate coating operation. Likewise possible is the direct addition of adhesion promoter substances to the coating composition with which the decorative and/or technically useful coating is to be produced. When using aqueous coating compositions, which are becoming more and more widespread in the coating of plastics as well, on environmental grounds, the adhesion problems between plastics substrate and coating composition are particularly striking.
Great problems are caused, for example, in the coating of plastics substrates such as, for example, polypropylene modified with ethylene-propylene-diene copolymers (PP-EPDM) and also polycarbonate modified with polybutadiene terephthalate (PC-PBT) and polyurethane (PUR-RIM). In accordance with the present state of knowledge, PP-EPDM substrates can be coated only after pretreatment by flaming. For PC-PBT and PUR-RIM substrates, no flaming is necessary. However, the wiping of the corresponding substrates with the solvents at least is necessary in order to achieve sufficient adhesion. Even after such pretreatment, however, the adhesion is not sufficient in all possible cases.